Originally Posted by idlewild (Post 2437086)

We recently had our ~300 sq ft. south-facing lanai enclosed with single pain / non-insulated glass on our ~1900 sq ft home. The wife wants "open living" (i.e. to keep the doors to the lanai open) and thought we could do it after we blew insultation into the lanai.

I'm concerned that not only are the new windows and door not double-paned (i.e. no insultation) but also the added space will strain our AC unit In fact, when I saw the price of a mini-split I figured we might be able to extend the existing ductwork into the lanai after insulating, but I was told from multiple contractors that this would strain the AC and is not to code.

Questions: even if we blew insultation, how much cool air would we be bleeding from the single-pain glass? With this leakage and new 300 sq feet to cool, how much of a load/strain would leaving the doors to the lanai open place on our AC unit and is that comparable to having the ducts directly into it?

My idea of "open living" is not keeping the doors open, but rather using the lanai occasionally with the doors open (i.e. air conditioning from the home) but mostly using it later at night with windows open for a breeze to naturally cool it, but I supposed we're going to have to minimally both blow insulation and get a mini-split if my wife wants to keep the doors open all the time, correct?

Originally Posted by Koapaka (Post 2437109)

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Originally Posted by retiredguy123 (Post 2437176)

What you said in your second sentence is not at all typical. The builder does not install insulation above the ceiling in either the lanai or the garage because these are unconditioned spaces. Most likely, there is no insulation above your lanai ceiling.

Originally Posted by treylagger (Post 2437229)

We just added a glassed in Cat 5 room to our west-facing lanai - about 220 square feet. Our situation is different though as it's insulated, low E, Argon glass. We raised the floor, removed the existing sliders and insulated the attic. We thought we'd need a mini split (around $6,500) but were able to get by with adding duct work to our existing 2.5 ton AC unit (around $1,800). Our room was finished a couple of days before we left for the summer but we monitor it (and other rooms) with ecobee Smart Sensors - the lanai's temp is the same as the rest of the house.

Originally Posted by mikreb (Post 2437201)

Do yourself a favor. Insulate and put in the mini-split you won't regret it. We've tried all the other options, 1. leave the slider open, place a fan in the doorway (still too hot) 2. portable ac (still too hot).

Mini-split, roll down shades and insulation is the way to go. We used Sun Kool, but Munn's is a good option as well.

Originally Posted by idlewild (Post 2437342)

Thanks for all the helpful information - especially the consideration of having the mini-split as a backup AC (although as we're in a brand new home, I'm hoping we won't ever need that)!

Here's a shocker (well, maybe not considering what I have experience thus far with TV construction):

Our home just under 2000 square feet and our Carrier HVAC is only 3 ton. I'm no HVAC expert - which is why I posted on here in the first place - but I checked with ChatGPT and even without adding another 300 square feet of space to cool in our lanai, our brand new home has a significantly undersized HVAC.

Here's the details:
Our HVAC is a Carrier, Model/Catalog Number: 27SPA636A003.

Using ChatGPT, I learned that "27SPA6" = Series and type of unit (in this case, part of Carrier's Performance series) and the next "36" is the key number to determining size. It indicates the BTU rating and "36" typically refers to 36,000 BTUs. If 12,000 BTUs = 1 ton, 36,000 BTUs = 3 tons. So we have a 3 ton system.

Following up, ChatGPT offered:

"✅ Conclusion:
Your Carrier 3-ton unit (27SPA636A003) should adequately cool a home between 1,200 and 1,500 square feet in ZIP 34762, assuming:
-Standard 8-foot ceilings
-Moderate insulation and window exposure
-No major heat loads (e.g., sunroom or uninsulated attic)

If your home is larger than 1,500 sq ft, this unit may:
-Struggle to maintain target temperatures on hot days
-Run continuously, increasing your electric bill
-Fail to adequately dehumidify

Let me know your exact square footage and house characteristics if you'd like a more tailored answer."

I replied that our square footage is 1967 square feet and we are considering adding a sun room (currently without cooling) which would be ~300 more square feet.


ChatGPT said:
"Thanks — that's very helpful.

������ Total Space to Potentially Cool:
Existing home: 1,967 sq ft

Planned sunroom: +300 sq ft

Total = ~2,267 sq ft

������ Location: ZIP 34762 (Okahumpka, FL – hot & humid)
������ Analysis:
Using Florida’s typical sizing of 400–500 sq ft per ton, here's the breakdown:

Cooling Load Estimate Tons Needed
2,267 ÷ 500 = ~4.5 tons
2,267 ÷ 450 = ~5 tons (more conservative)

Your current 3-ton unit (Carrier 27SPA636A003) is significantly undersized for this total area, especially with the sunroom added.

������ Recommendation:
Option Use Case
5-ton unit Ideal for full-home + sunroom cooling in a Florida climate.
Dual-zone system (e.g. 3-ton + mini-split for sunroom) If replacing the main unit isn’t ideal. Helps avoid oversizing the main system and improves efficiency.
4-ton unit (only if you don’t cool sunroom) Bare minimum for 1,967 sq ft, but borderline in FL. May underperform during peak heat.

✅ Final Answer:
You should upgrade to a 5-ton HVAC system (or add a mini-split to cool the sunroom separately) to adequately and efficiently cool a 2,267 sq ft home in Florida. A 3-ton system will not keep up, especially in July–August, and will wear out faster from overwork.

Let me know if you’d like help comparing Carrier 5-ton systems or mini-split options for the sunroom."

Can any HVAC experts add color here? Are TV 3 ton HVACs undersized for Florida's hot humid climates?

Originally Posted by jrref (Post 2437351)

Generally, you need 20 BTU for every square foot of space in your home. The chart below can guide your BTU choice:

Home Square Footage BTU (British Thermal Unit) Tonnage
600 – 1,000 18,000 1.5
1,000 – 1,300 24,000 2
1,300 – 1,600 30,000 2.5
1,600 – 1,900 36,000 3
1,900 – 2,200 42,000 3.5
2,200 – 2,600 48,000 4
2,600 – 3,200 60,000 5
The larger your home, the higher BTU you’ll need to support your comfort. One of the most accurate ways to measure the right size AC for your home is with a Manual J calculation.

So you AC is sized correctly.

Originally Posted by Micizel (Post 2437282)

We are thinking of doing what you just did with raising the floor and removing the sliders inside. We have a mini split. We’re already glassed in with old screen and sliders but want to remove them with solid glass. Can you share who you used for the work?